Re: Syntax question

On Mar 3, 2010, at 9:51 AM, Cameron Ross wrote:

> Hi,
>
> Its not readily apparent from the PowerLoom documentation how to  
> interpret :=>>.  Enlightenment would be very much appreciated.

The extra > on the arrow heads are used for inference direction control.

Normally, with a rule like

    (A ?x)  :=> (B ?x)

PowerLoom is free to run this rule either in a forward direction or a  
backward direction.  Running it forward means that if we assert (A  
i-1) then we immediately conclude (B i-1).  Running backward means  
that if we are trying to prove (B i-1) or find (B ?x) then we look to  
see if (A i-1) is already known.

When extra arrow heads are used, this tells PowerLoom the desired  
direction of the rule, so that

   (A ?x)  :=>>  (B ?x)

will be run only in the forward direction.  This gives some additional  
inference control and affects both what will be inferred as well as  
the performance of the reasoner.